Intraspecific differentiation in Helix aspersa Müller, which essentially occurred in North Africa, was until now investigated using only conchological and biochemical features. In this study, 972 specimens were scored for 10 metric characters (nine describing the terminal genitalia, one which represents the shell size) in order to complement our knowledge of the geographic patterns of divergence between populations from the whole natural area of the species. Multivariate analyses, involving principal components and discriminant functions, emphasized the high degree of differentiation in Maghreb (east versus west pattern) and indicated that the most reliable anatomical features to distinguish individuals, which generally have a giant size in North Africa, were the penis and diverticulum (to a lesser extent, flagellum) lengths. Thus, snails from eastern Maghreb were characterized by the smallest distal genitalia, especially a short diverticulum, although their shell size was far larger than that of European snails. This reduction was less perceptible in specimens from west Maghreb and, when present, concerned only some organs; penis length, not affected by this decrease, became then an important factor of discrimination in Maghreb. Moreover, it seemed that a large part of anatomical divergence between European and north-western African populations was only attributable to a difference in shell size (larger snails with larger genitalia), whereas isolation of populations from eastern Maghreb was based on independent changes, involving different allometric relations between terminal genitalia and shell size. Furthermore, this phenomenon was observed in colonies from north-western Greece, which were also close to some populations from east Maghreb on the basis of allozyme data; such results would suggest exchanges between both areas.